GB1051140A - - Google Patents

Abstract

1,051,140. Detecting particles in fluids. UNITED RESEARCH Inc. Oct. 30, 1963, No. 42760/63. Heading GIN. In an apparatus for detecting foreign particles in a fluid e.g. in petrol, the fluid forms the dielectric of a sensing capacitor 32 (Fig. 3) and variation of the capacitance due to a particle shifts the resonant frequency of a resonant circuit 32, 34, 36, 38 which is excited by a crystal controlled fixed frequency oscillator 42 and hence changes the voltage at the oscillator frequency on line 50. The oscillator frequency is preferably chosen to lie on a linear portion of the resonance curve Fig. 4 (not shown), preferably close to either extreme of the bandwidth of the resonance curve in absence of a particle. A voltage output from the L.C. circuit applied to a peak detector circuit 55 the output signal from which is fed to an A. C. amplifier 64 and comprises a direct voltage whose amplitude corresponds to the output of the L. C. circuit when no particles are present, having superimposed thereon pulses of polarity depending on the dielectric constant of particles producing them. The pulses only are amplified and the D. C. component is blocked. The output from the amplifier may be fed through a coupling transformer 70, 72 to a pulse counter 78 or alternatively to an averaging circuit including resistor 83 and capacitor 84, the output signal from which will represent the average, over a period of time determined by the time constant of the averaging circuit, of the area and number of pulses supplied to it. The pulse area in turn is dependent on the size of the particle and the output signal is a measure of the total concentration of contaminant whose dielectric constant is greater than that of the fluid. A second averaging circuit may be provided for particles of lower dielectric constant than the fluid. SENSING ELEMENT. (Fig. 1) and Fig. 2 (not shown). The sensing element 4 which is positioned in a fluid transfer pipe 2 includes a non conducting portion 6 e.g. "Teflon" (*Registered Trade Mark), and an annular conductive band 8, e. g. brass, a central non-conductive body portion 10 e.g. Teflon, and an end portion 12. The body portions are clamped together by an arial bolt; and the element is supported on struts 14. The band 8 forms one electrode and the pipe or a conductive band 22 in the pipe 2 (if the pipe is non conductive) forms the other electrode. The particles are sensed as they pass through an annular orifice formed between bands 8 and 22. Component values are exemplified.